This invention relates generally to improvements in hydraulically powered percussion drills. More particularly, but not by way of limitation, this invention relates to an improved hydraulically powered percussion drill that will not become stalled when the drill is run free, that is, when the reciprocating striker piston is not engaging the drill steel.
The invention described hereinafter is an improvement to the hydraulically powered percussion drill described in U.S. Pat. No. 3,701,386, issued Oct. 31, 1972 to Jacob E. Feucht. The hydraulically powered percussion drill or hydraulic drifter as it is sometimes referred to described therein operates in a satisfactory manner except that it is desirable to be able to reciprocate the striker piston within the housing to impart vibrations to the drill steel when the striker piston is not actually engaging the drill steel. With the device described in the patent, the striker piston occasionally becomes stalled in the lowermost position when running free. It is frequently desirable to impart vibrations to the housing when retracting the drill to change drill steels, removing stuck steels from the hole being drilled and adding or removing drill steel sections.
Accordingly, it is one object of this invention to provide an improved hydraulically actuated percussion drill that will operate to provide vibration to the housing when the drill is running free.
Another object of the invention is to provide an improved hydraulically powered percussion drill that can be run free and that includes overtravel protection to prevent damage to the drill.